As hard films having high-temperature oxidation resistance, various hard films of AlCr were proposed. Japanese Patent 3027502 discloses a wear-resistant amorphous hard film with high-hardness having a composition represented by the general formula of (AlaMb)100-cXc, wherein M is at least one element selected from the group consisting of Ti, Ta, V, Cr, Zr, Nb, Mo, Hf, W. Fe, Co, Ni, Cu and Mn, X is at least one element selected from the group consisting of N, O and C, and a, b and c are atomic % meeting 60%≦a 98.5%, 1.5%≦b≦40%, 0%<c≦65%, and a+b=100%. However, this amorphous film has a Knoop hardness of about 21 GPa at most, insufficient in wear resistance and adhesion.
Japanese Patent 3039381 discloses a method comprising generating a vapor mixture of Al and Cr from a target composed of 25–50 atomic % of Al and 75–50 atomic % of Cr disposed in a vacuum chamber by arc discharge, and simultaneously introducing a nitrogen gas into the vacuum chamber to cause a reaction between the vapor mixture and the nitrogen gas, thereby forming an Al—Cr—N composite hard film having excellent high-temperature oxidation resistance that prevents oxidation even at 800–900° C. on a substrate. Also, JP 2002-160129 A discloses a method for surface-treating a tool, comprising forming an intermediate layer of Ti, Cr, Si or Al on a substrate surface, and coating the intermediate layer with a hard film of AlCrN. These hard films are made of AlCr nitride having a high-temperature oxidation resistance of about 1000° C. However, they do not have oxidation resistance exceeding 1000° C. Further, these hard films had as insufficient hardness Hv as about 21 GPa, poor in wear resistance.